Foot and mouth disease (FMD) is one of the most contagious, acute viral diseases of cloven-footed animals such as cattle, sheep, goats and pigs (Brown, 2003). FMD is caused by foot and mouth disease virus (FMDV), belongs to Aphthovirus genus in the family Picornaviridae. Airborne transmission is the common method of spread while the disease also spreads through fomites. FMD is controlled by stamping out method in non-endemic countries and by vaccination in endemic countries (Grubman and Baxt, 2004).
Current conventional vaccine is an inactivated whole-virus preparation (Doel, 2003). The difficulties involved in differentiating vaccinated from infected animals have kept many countries away from adopting the strategy of FMD vaccination as primary method of control. It is necessary to differentiate vaccinated animals from infected animals using a reliable and accurate diagnostic test if non-endemic countries can consider vaccination as a method of control during an outbreak.
Antibodies principally to the structural proteins of FMDV are induced in vaccinated animals, whereas infected animals produce antibodies to both structural and non-structural proteins (NSP) (Sun et al., 2004). Therefore, assays demonstrating antibodies against non-structural proteins have potential to differentiate infected animals from those that have been vaccinated. The antibodies against polyprotein 3ABC have been proved to be the most reliable marker of FMDV infection. ELISA utilizing recombinant proteins produced either in E. coli or baculovirus are used to distinguish the vaccinated animals from infected animals (De Diego et al., 1997; Mackay et al., 1998; Sorensen et al., 1998; Shen et al., 1999; Kitching., 2002; Chung et al., 2002; Clavijo et al., 2004a, 2004b; Sorensen et al., 2005; Robiolo et al., 2005; Niedbalski, 2005). Specificity of 2C and 3D polypeptides were also tested, but were found to be less sensitive when compared to 3ABC polypeptide (Sorensen et al., 1998; Jae Ku Oem et al., 2005).
Shen et al. (1999) used synthetic peptides containing B-cell epitopes of FMDV non-structural proteins and reported that the immunoreactivity to 2C peptides was primarily to those from N-terminal region of the protein. Further recently, the overlapping synthetic peptides were used to identify FMDV infection-specific linear B-cell epitopes to differentiate infected from vaccinated cattle (Hohlich et al., 2003; Sun et al., 2004). Indirect ELISA based on a long (57 amino acid) synthetic peptide was used by Shen et al., (1999), but synthesis of long peptides is difficult. Therefore, short peptide of 20 amino acids was suggested by Hohlich et al. (2003) which has inherent problems due to their weak binding to solid surface. This is the main factor that affects the efficiency and sensitivity of solid phase immunoassay using synthetic peptide as an antigen.
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